spec.js

describe 'Perfect Numbers'
  
  it 'should find 6 in a range between 2 and 10'
    findPerfectNumbersInRange(2,10, function(result){
      result.should.eql [6]
    });  
  end
  it 'should return 28 in a range between 20 and 30'
    findPerfectNumbersInRange(20, 30, function(result){
      result.should.eql [28]
    });
  end 
  it 'should return 496 in a range between 200 and 500'
    findPerfectNumbersInRange(200, 500, function(result){
      result.should.eql [496]
    });
  end

  it 'should find all perfect numbers in the range 2 to 900'
    findPerfectNumbersInRange(2, 900, function(result){
      result.should.eql [6, 28, 496]
    });
  end
end

yourlib.js

function findPerfectNumbersInRange(start, end, fnc){
  var results = [];  
  (function(num){
    perfectNumber(num, function(num){
      results.push(num);    
    });
    if(num++ < end) arguments.callee(num)
    return function(){ fnc(results)}
  })(start)();
}

function perfectNumber(i, fnc){
    var result = 0;
    for( var j = 0; j < i; j++ ) {
      if(i % j == 0) result += j;
    }
    if( result == i) fnc(result);
}